1. Field of the Invention
This invention relates to an engine supporting device for a motorcycle for suspending a cylinder head of an engine with a hanger bracket mounted to a frame, and particularly to the mounting structure of the hanger bracket.
2. Description of Related Art
In a motorcycle with an engine having a standing cylinder section, a hanger bracket for suspending the cylinder section is mounted to a frame member passing above the cylinder section. The hanger bracket protrudes downwardly from the frame member and is connected, at the lower end, to the upper end of the cylinder section.
The frame member supporting the hanger bracket connects a main pipe extending rearwardly from a steering head pipe and a rear arm bracket for supporting a rear arm therebetween. A conventional frame member has an upper plate and a lower plate. The upper and lower plates are welded, with their edges in abutment against each other, to be formed in a hollow, box-like shape, and a pair of collars are welded to the lower end of the lower plate. The hanger bracket is fixed to the collar of the lower plate through bolts.
In a conventional device, the hanger bracket for suspending the cylinder section is subjected to a primary vibration of the engine. Since this vibration is transmitted to a frame member for supporting the hanger bracket, rigidity of the frame member has to be secured sufficiently for the engine to be suspended firmly.
However, since in conventional frame members, the upper and lower plates are made from sheet metal stamping parts or cast products, deformation can be produced when a large load is applied. Therefore, particular reinforcement measures have to be taken such as increasing the thickness of the upper and lower plates.
Therefore, the mounting portion of the hanger bracket becomes heavier and larger, resulting in an adverse affect on the moving performance of the motorcycle.
In view of the foregoing, an advantage of this invention is to provide an engine supporting device for a motorcycle in which the mounting portion of a hanger bracket can be formed light and compact.